Human fast-1 gene

ABSTRACT

hFAST-1 is a human forkhead activin signal transducer gene. The hFAST-1 protein has the ability to bind to human Smad2 and activate an activin response element (ARE). The hFAST-1-dependent activation of ARE is dependent on endogenous Smad4 and stimulation of the TGF-β receptor. The hFAST-1 protein binds to a novel DNA motif, TGT(G/T)(T/G)ATT, which is present within the ARE. This motif is important for the activation of genes responsive to ligands of the TGF-β family. The invention includes tools for investigating the TGF-β signaling pathway and screening for compounds which modulate the action of TGF-β.

The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of USPHS grant CA43460 awarded by the National Institutes of Health.

TECHNICAL FIELD OF THE INVENTION

The invention is related to the area of developmental and cancer genetics. In particular it is related to the field of transcriptional regulation.

BACKGROUND OF THE INVENTION

Substantial progress in understanding the responses to tumor-derived growth factor-β (TGF-β) and related ligands has been made in the last five years (Derynck and Fang, 1997; Hoodless and Wrana, 1998; Kretzschmar and Massague, 1998). The receptors for these ligands have been cloned and shown to be serine/threonine kinases which are activated by binding to ligand. The major substrates for these kinases, besides the receptors themselves, appear to be Smad proteins. The founding member of the Smad family is the product of the Drosophila gene Mad, identified by its requirement in signaling by the TGF-β family member Dpp (Sekelsky et al., 1995). Nine homologs of Mad have since been identified in vertebrate cells and shown to transduce or inhibit signals from specific TGF-β like ligands (Heldin et al., 1997; Derynck and Fang, 1997; Hoodless and Wrana, 1998; Kretzschmar and Massague, 1998).

The phosphorylation of Smad1, Smad2, and Smad3 stimulates their interaction with Smad4 and the transport of the resulting heteromeric complex to the nucleus (Kretzschmar et al., 1997; Lagna et al., 1996; Liu, 1997; Macias-Silva et al., 1996; Nakao et al., 1997; Nakao et al., 1997; Souchelnytskyi et al., 1997). Once in the nucleus, the Smad complex transcriptionally activates specific target genes through activation domains present at the carboxyl termini of these proteins (Liu et al., 1996). Two ways in which Smad activation could lead to transcriptional activation have been identified. First, it has been shown that human Smad3 and Smad4, but not Smad2, can bind to specific DNA sequences and activate transcription of adjacent reporters (Zawel et al., 1998). A similar sequence-specific activity is present in Drosophila Mad (Kim et al., 1997). Second, Smad2 has been shown to bind to the Xenopus forkhead activin signal transducer protein FAST-1 (xFAST-1) and to participate in a complex exhibiting sequence specific binding activity attributable to the xFAST-1 component (Chen et al., 1996; Chen et al., 1997; Liu, 1997). Although Smad4 does not directly bind to xFAST-1, Smad4 is recruited to the xFAST-1/Smad2 complex by Smad2 (Chen et al., 1997; Liu, 1997).

TGF-β-like responses are remarkably widespread in eukaryotes, and are important not only in development but also in cancer (Fynan and Reiss, 1993; Hartsough and Mulder, 1997). Further progress in understanding the varied developmental and oncogenic ramifications of these pathways in mammalian cells depends on knowledge of the relevant mammalian genes. Thus, there is a need in the art for the identification, isolation, purification, and analysis of mammalian and human genes which mediate physiological and pathological responses to TGF-β and related ligands.

SUMMARY OF THE INVENTION

It is an object of the invention to provide reagents and methods for altering TGF-β activity. These and other objects of the invention are provided by one or more of the embodiments described below.

One embodiment of the invention provides an isolated and purified hFAST-1 protein comprising the amino acid sequence shown in SEQ ID NO:2 and naturally occurring biologically active variants thereof.

Another embodiment of the invention provides a fusion protein which comprises a first protein segment and a second protein segment fused to each other by means of a peptide bond. The first protein segment consists of at least thirteen contiguous amino acids selected from the amino acid sequence shown in SEQ ID NO:2.

Still another embodiment of the invention provides an isolated and purified polypeptide which consists of at least thirteen contiguous amino acids of hFAST-1 as shown in SEQ ID NO:2.

Even another embodiment of the invention provides a preparation of antibodies which specifically bind to an hFAST-1 protein as shown in SEQ ID NO:2.

Yet another embodiment of the invention provides a subgenomic polynucleotide which encodes an hFAST-1 protein as shown in SEQ ID NO:2.

Still another embodiment of the invention provides a vector comprising a subgenomic polynucleotide which encodes an hFAST-1 protein as shown in SEQ ID NO:2.

Another embodiment of the invention provides a vector comprising a subgenomic polynucleotide which encodes an hFAST-1 protein as shown in SEQ ID NO:2 and which is intron-free.

Yet another embodiment of the invention provides a vector comprising a subgenomic polynucleotide which comprises the sequence shown in SEQ ID NO:1.

Even another embodiment of the invention provides a recombinant host cell which comprises a polynucleotide. The polynucleotide encodes an hFAST-1 protein as shown in SEQ ID NO:2.

Still another embodiment of the invention provides a recombinant host cell which comprises a polynucleotide. The polynucleotide encodes an hFAST-1 protein as shown in SEQ ID NO:2 and which is intron-free.

Yet another embodiment of the invention provides a recombinant host cell which comprises a polynucleotide. The polynucleotide comprises the sequence shown in SEQ ID NO: 1.

A further embodiment of the invention provides a recombinant DNA construct for expressing hFAST-1 antisense nucleic acids. The recombinant DNA construct comprises a promoter and a coding sequence for hFAST-1. The coding sequence consists of at least 12 contiguous base pairs selected from SEQ ID NO:1. The coding sequence is in an inverted orientation with respect to the promoter. Upon transcription from the promoter an RNA is produced which is complementary to native mRNA encoding hFAST-1.

Another embodiment of the invention provides a method of screening test compounds for those which inhibit the action of TGF-β. A test compound is contacted with a first protein and a second protein. The first protein is all or a portion of a Smad2 protein or a naturally occurring biologically active variant thereof. The portion of the Smad2 protein is capable of binding to hFAST-1. The second protein is all or a portion of hFAST-1 or a naturally occurring biologically active variant thereof. The portion of hFAST-1 is capable of binding to the portion of the Smad2 protein. An amount selected from the group consisting of (a) the first protein bound to the second protein, (b) the second protein bound to the first protein, (c) the first protein which is not bound to the second protein, and (d) the second protein which is not bound to the first protein is determined. A test compound which decreases the amount of (a) or (b) or increases the amount of (c) or (d) is a candidate compound for inhibiting the action of TGF-β.

Even another embodiment of the invention provides a method of screening test compounds for the ability to decrease or augment TGF-β activity. A cell is contacted with a test compound. The cell comprises a first fusion protein, a second fusion protein, a reporter gene, and hSmad4 protein. The first fusion protein comprises (1) a DNA binding domain or a transcriptional activating domain and (2) all or a portion of an hFAST-1 protein. The portion of hFAST-1 consists of a contiguous sequence of amino acids selected from the amino acid sequence shown in SEQ ID NO:2. The portion of hFAST-1 is capable of binding to Smad2 protein. The second fusion protein comprises (1) a DNA binding domain or a transcriptional activating domain and (2) all or a portion of Smad2 protein, or a naturally occurring biologically active variant thereof. The portion of Smad2 is capable of binding to hFAST-1 protein. When the first fusion protein comprises a DNA binding domain, the second fusion protein comprises a transcriptional activating domain. When the first fusion protein comprises a transcriptional activating domain, the second fusion protein comprises a DNA binding domain. The interaction of the portion of the hFAST-1 protein with the portion of Smad2 protein reconstitutes a sequence-specific transcriptional activating factor. The reporter gene comprises a DNA sequence to which the DNA binding domain of the first or second fusion protein specifically binds. The expression of the reporter gene is measured. A test compound which increases the expression of the reporter gene is a potential drug for increasing TGF-β activity. A test compound which decreases the expression of the reporter gene is a potential drug for decreasing TGF-β activity.

Still another embodiment of the invention provides a method of screening for drugs with the ability to decrease or augment TGF-β activity. A cell is contacted with a test compound and with TGF-β. The cell comprises all or a portion of Smad2 protein or a naturally occurring biologically active variant thereof and all or a portion of hFAST-1 or a naturally occurring biologically active variant thereof. The portion of Smad2 protein is capable of binding to hFAST-1. The portion of hFAST-1 is capable of binding to Smad2 protein. The cell also comprises a vector and hSmad4 protein. The vector comprises a reporter gene under the control of an activin response element. The activin response element comprises a DNA motif TGT(G/T)(T/G)ATT as shown in SEQ ID NO:4. Transcription of the reporter gene is measured. A test compound which increases the amount of reporter gene transcription is a potential drug for augmenting TGF-β activity. A test compound which decreases the amount of reporter gene transcription is a potential drug for decreasing TGF-β activity.

Another embodiment of the invention provides a recombinant construct which comprises a reporter gene under the control of an activin response element. The activin response element comprises an hFAST-1 binding motif TGT(G/T)(T/G)ATT as shown in SEQ ID NO:4.

A further embodiment of the invention provides a double-stranded DNA fragment which comprises an activin response element. The activin response element comprises an hFAST-1 binding motif TGT(G/T)(T/G)ATT as shown in SEQ ID NO:4. The fragment is covalently attached to an insoluble polymeric support.

Even another embodiment of the invention provides an isolated and purified oligonucleotide which encodes at least thirteen contiguous amino acids of hFAST-1 protein as shown in SEQ ID NO:2.

Yet another embodiment of the invention provides an isolated and purified oligonucleotide which comprises at least 19 contiguous nucleotides of hFAST-1 as shown in SEQ ID NO: 1.

The invention thus provides the art with novel tools and systems with which to probe and modify the molecular events of the TGF-β signal transduction pathway which result in transcriptional activation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays the sequence of hFAST-1 and compares it to the Xenopus homolog. Conserved amino acids are shaded. The forkhead domain encompasses xFAST-1 residues 108 to 219 (Chen et al., 1996). The C-terminal Smad-interacting domain (SID) encompasses xFAST-1 residues 380 to 506 (Chen et al., 1997).

FIG. 2 illustrates the expression of hFAST-1 and its interaction with Smad2. FIG. 2A demonstrates that hFAST-1 was expressed in all tissues tested. RNA samples prepared from the indicated tissues were used as templates for RT-PCR analysis. The PCR primers used span a 100-bp intron and discriminate the spliced (423 bp) and unspliced (523 bp) RT-PCR products. The unspliced products arose from either genomic DNA or from unprocessed transcripts. FIG. 2B shows that both full-length hFAST-1 (FAST-FL) and its carboxyl-terminus (FAST-SID) could interact with the carboxyl-terminal (MH2) domain of Smad2 in vitro. Polypeptides encoding full-length hFAST1 or its SID domain were generated by in vitro translation in the presence of ³⁵S-labeled methionine and incubated with a GST-fusion protein containing the carboxyl terminus of Smad2 (GST-Smad2/MH2) immobilized on agarose beads. An irrelevant protein (PIG3, Polyak et al., 1997) was also translated and incubated with GST-Smad2MH2 as a control. After extensive washing, the bound proteins were eluted and separated in a 4-20% SDS-Tris-glycine gel which was dried and autoradiographed. Ten percent of the in vitro translated proteins used for binding to Smad2 were applied to the lanes labeled “Total.”

FIG. 3 demonstrates hFAST-1 mediated transcriptional activation. FIG. 3A shows that hFAST-1 mediated transcriptional activation requires TGF-β. MvLu1 cells were transfected with pAR3-lux with or without pCMV-hFAST-1 (FAST-1). The transfected cells were cultured in the presence or absence of TGF-β1 (1 ng/ml). Twenty hours following transfection, cells were harvested and luciferase activity measured. The results were normalized to the control in which cells were neither transfected with pCMV-hFAST-1 nor treated with TGF-β. Bars and brackets represents the means and standard deviations calculated from triplicate transfections. FIG. 3B shows that activin signaling leads to hFAST-1 mediated transcriptional activation. HCT116 cells were cotransfected with pAR3-lux, pCMV-hFAST-1 (FAST-1), and the constitutively active activin receptor ActRIB* as indicated. Luciferase activity was analyzed 20 hours later and the results normalized to controls transfected with reporter but without pCMV-hFAST-1 or ActR1B*. FIG. 3C demonstrates that hFAST-1-mediated transcriptional activation requires Smad4 and a functional hFAST-1 forkhead domain. HCT116 cells or their Smad4-deficient derivatives (5-18) were transfected with pAR3-lux plus pCMV-hFAST-1 (wt [FAST-1] or mutant H83R [FAST-1]) plus the RII receptor for TGF-β as indicated. All cells were treated with TGF-β1 for 20 hours prior to harvest. Luciferase activity was normalized to the control in which cells were not transfected with pCMV-hFAST-1 or RII.

FIG. 4 demonstrates the sequence-specific DNA binding of hFAST-1. FIG. 4A shows examples of an electrophoretic mobility shift analysis (EMSA) of mock-selected or hFAST-1-selected clones. ³²P-labeled PCR products generated from individual clones were incubated with a GST-fusion protein containing full length hFAST-1 sequences. Derivation of clones and EMSA were performed as described in Example 7. Mock selected clones were used for comparison (“C” lanes). The positions of free probe and hFAST-1 bound probe (“shift”) are indicated. FIG. 4B provides a sequence summary of clones that bound to hFAST-1. The sequences of the relevant segment of 17 hFAST-1-binding clones were determined and the fractions of clones containing the nucleotides at the indicated positions relative to the consensus are shown. FIG. 4C demonstrates the binding of FBE to hFAST-1. Wild-type (FBE) or mutant (FBE*) oligonucleotides were incubated with 0.5-2.0 μg of GST fusion proteins containing full-length hFAST-1 (FAST-FL) or only its forkhead domain (FAST-FH). GST fusion proteins containing the MH1 or MH2 domains of Smad2 (S-N and S-C, respectively; Zawel et al., 1998) were used as controls. The FBE* oligonucleotide contained the sequence TCTGTATC in place of the consensus TGTGTATT but was otherwise identical to FBE. FIG. 4D demonstrates the binding of ARE oligonucleotides to hFAST-1. EMSA was performed with (+) or without (−) 1 μg of GST fusion protein containing full length FAST-1 (“FAST-FL”). The sequence of the 50 bp ARE oligonucleotide differed by only one bp from ARE*.

DETAILED DESCRIPTION OF THE INVENTION

We have isolated and characterized a human homolog of Xenopus FAST-1, termed hFAST-1. hFAST-1 mediates transcriptional responses to TGF-β and activin in a ligand-, receptor-, and Smad-dependent fashion.

hFAST-1 protein consists of 365 amino acid residues which are shown in SEQ ID NO:2 and FIG. 1. A nuclear localization domain is found at residues 22-30, and the adjacent downstream region (approximately residues 33-154) is presumed to contain the forkhead DNA-binding domain. The Smad2 binding domain is found near the carboxy terminus.

The invention also includes naturally occurring biologically active variants of hFAST-1. Naturally occurring biologically active variants of hFAST-1 include proteins which have, for example, conservative amino acid substitutions of amino acids of SEQ ID NO:2. Such variants can result, for example, from polymorphisms in an hFAST-1 coding sequence. Biologically active variants of hFAST-1 possess similar biological activity to that of the hFAST1 protein shown in SEQ ID NO:2, such as the ability to bind to Smad 2, to bind to the ARE binding motif of SEQ ID NO:4, and to activate transcription.

hFAST-1 polypeptides consist of at least 13, 14, 15, 17, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 87, 88, 100, 120, 140, 144, 145, or 150 contiguous amino acids of hFAST-1 as shown in SEQ ID NO:2. Polypeptides can also comprise regions of the hFAST-1 amino acid sequence which are involved in the binding of hFAST-1 to Smad2. Such regions are located near the carboxy terminus of hFAST-1, e.g., in the region from positions 277-364 or 221-365 of SEQ ID NO:2. Polypeptides can also comprise the nuclear localization region of hFAST-1, amino acids 22-30. An hFAST-1 protein or polypeptide can be isolated by physical separation from the cells in which it is produced and separation from most of the other proteins produced by the cells. Standard purification techniques such as affinity or ion exchange chromatography, as well as any other technique known in the art, can be used to purify the protein or polypeptide. A protein or polypeptide preparation is purified when it exists as a nearly homogeneous mixture consisting of at least about 70, 75, 80, 85, 90, 95, 98, or 99% of the desired molecular species.

hFAST-1 protein or polypeptides can also be produced by recombinant DNA methods or by synthetic chemical methods. For production of recombinant hFAST-1 protein or polypeptides, for example, the coding sequence shown in SEQ ID NO:1 can be expressed in known prokaryotic or eukaryotic expression systems. Bacterial, yeast, insect, or mammalian expression systems can be used, as is known in the art. Alternatively, synthetic chemical methods, such as solid phase peptide synthesis, can be used to synthesize an hFAST-1 protein or polypeptide.

The invention also provides non-naturally occurring fusion proteins which comprise all or a portion of hFAST-1. In such a fusion protein, a first protein segment is fused to a second protein segment by means of a peptide bond. The first protein segment consists of at least 13, 14, 15, 17, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 87, 88, 100, 120, 140, 144, 145, or 150 amino acids of hFAST-1 as shown in SEQ ID NO:2. The second protein segment can be all or a portion of any protein whose structure or function is desired to be combined with that of hFAST-1. An hFAST-1 fusion protein can be produced by using standard recombinant DNA techniques to combine the sequences of the desired first and second protein segments into an expression vector, which is introduced into a cell or cell line that is subsequently induced to express the fusion protein. The fusion protein may either be used within the cell or cell line containing the vector or it can be isolated and optionally purified from the cell or cell line, or from the culture medium, using standard cell homogenization, extraction, and protein purification methods.

Antibodies can be prepared which specifically bind to epitopes of an hFAST-1 protein, polypeptide, or fusion protein. Such antibodies can be immunoglobulins of any class, i.e., IgG, IgA, IgD, IgE, or IgM. The antibodies can be obtained by immunization of a mammal such as a mouse, rat, rabbit, goat, sheep, primate, human, or other suitable species. The antibodies can be whole immunoglobulins or fragments thereof, provided that specific binding for hFAST-1 epitopes is maintained. Antibodies to hFAST-1 can be the result of genetic engineering, e.g., interspecies or chimeric antibodies. The antibodies can be polyclonal antibodies which are obtained from the serum of an immunized animal, i.e., antiserum. The antibodies can also be monoclonal antibodies, formed by immunization of a mammal with an hFAST-1 antigen, fusion of lymph or spleen cells from the immunized mammal with a myeloma cell line, and isolation of specific hybridoma clones, as is known in the art.

hFAST-1 antibodies can, if desired, be purified by any method known in the art, e.g., affinity purification using a column with hFAST-1 antigen as the affinity ligand. The antibodies can be eluted from the column, for example, using a buffer with a high salt concentration.

Antibodies which specifically bind to hFAST1 proteins, polypeptides, or fusion proteins provide a detection signal at least 5-, 10-, or 20-fold higher than a detection signal provided with other proteins when used in Western blots or other immunochemical assays. Preferably, antibodies which specifically bind to hFAST-1 epitopes do not detect other proteins in immunochemical assays and can immunoprecipitate a hFAST-1 protein, polypeptide, or fusion protein from solution.

The invention also provides isolated subgenomic polynucleotides which encode hFAST-1 protein and polypeptides. Subgenomic polynucleotides contain less than a whole chromosome. Preferably, the polynucleotides are intron-free. One subgenomic polynucleotide encodes the hFAST-1 protein shown in SEQ ID NO:2. hFAST1 polynucleotide molecules can also comprise a contiguous sequence of at least 10, 11, 12, 15, 19, 20, 25, 30, 32, 35, 37, 40, 45, 50, 60, 70, 74, 80, 90, or 100 nucleotides selected from SEQ ID NO: 1. Optionally, a subgenomic polynucleotide can comprise the nucleotide sequence of SEQ ID NO:1.

The complement of the nucleotide sequence shown in SEQ ID NO:1 is a contiguous nucleotide sequence which forms Watson-Crick base pairs with a contiguous nucleotide sequence shown in SEQ ID NO:1 and is also a subgenomic polynucleotide, which can be used to provide hFAST-1 antisense oligonucleotides. A double-stranded polynucleotide which comprises the nucleotide sequence shown in SEQ ID NO:1 is also a subgenomic polynucleotide.

Isolated and purified oligonucleotides which encode at least 13 contiguous amino acids of hFAST1 protein as shown in SEQ ID NO:2, or which comprise at least 19 contiguous nucleotides of SEQ ID NO:1, are also included as subgenomic polynucleotides.

The hFAST-1 gene can be isolated by the method described in Example 1. The gene is isolated when it is obtained free from unrelated polynucleotide sequences, leaving only coding, non-coding, and regulatory sequences associated with the expression of hFAST-1 protein.

hFAST-1 subgenomic polynucleotides can be isolated and purified free from other nucleotide sequences using standard nucleic acid purification techniques. For example, restriction enzymes and probes can be used to isolate polynucleotide fragments which comprise nucleotide sequences encoding hFAST-1 protein. Isolated and purified subgenomic polynucleotides are in preparations which are free or at least 90% free of other molecules. Optionally, hFAST-1 subgenomic polynucleotides can contain sequences from non-coding regions of the hFAST-1 gene, such as introns, or sequences from a promoter region or transcription terminator region.

In order to clone, replicate, modify, express, or otherwise manipulate hFAST-1 subgenomic polynucleotides, sequences of hFAST-1 can be incorporated into a recombinant construct. A recombinant construct can be a linear or circular polynucleotide, e.g., a viral DNA or RNA or a plasmid. Optionally, a recombinant construct is capable of transferring desired nucleotide sequences into a prokaryotic or eukaryotic cell. The construct can be a vector and can contain additional nucleotide sequences such as replication origins, promoters, transcription terminators, and reporter genes to facilitate replication, insertion into the host cell genome, expression, or detection of the vector. For example, an expression vector can comprise a promoter capable of activating expression in a host cell.

Vectors or recombinant constructs can be prepared by standard recombinant DNA techniques. Vectors or other recombinant constructs containing either native or modified hFAST-1 sequences or fragments thereof can optionally contain sequences from other proteins so as to create fusion proteins or can contain reporter gene sequences. Protein sequences which serve as portions of fusion proteins or as reporter genes can be from any human or non-human protein. Any reporter gene, such as the genes for green fluorescent protein (GFP), luciferase, chloramphenicol acetyltransferase, or β-galactosidase, can be incorporated into such vectors or constructs in order to facilitate determination of the level or localization of expression of hFAST-1 proteins or polypeptides. The expression of such reporter genes can be detected, for example, as fluorescence or as enzyme activity or by standard immunocytochemical techniques.

hFAST-1 subgenornic polynucleotides can be incorporated into an expression vector which is then used to transfect an appropriate cell line, and used to produce hFAST-1 protein, polypeptides, or fusion proteins containing all or a portion of hFAST-1. Using the sequence information for hFAST-1 shown in SEQ ID NOS:1 and 2, variants of hFAST-1 can be constructed which retain all or a portion of the biological activity of hFAST-1.

A vector can be introduced into a suitable host cell by standard transfection techniques, to produce a recombinant host cell. Transfection with an hFAST-1 vector can be either transient or stable, as required by the particular needs of an hFAST-1 expression protocol.

The recombinant host cell is a cell or cell line which is suitable for transfection by the vector and for expression of the hFAST-1 protein or polypeptide. Many different cell types are suitable as the recombinant host cell. Examples of such cells are the cells of bacteria, yeast, insects, amphibians, and mammals, such as a mouse, rat, primate, human, or other suitable species. Recombinant host cells can also be tumor cells grown either in cell culture or in an animal, such as a nude mouse.

The orientation of hFAST-1 coding sequences in a recombinant construct or an expression vector relative to promoter and transcription terminator sequences can be as found in the native hFAST-1 gene or can be inverted so as to allow the production of hFAST-1 antisense oligonucleotides. If coding sequences are utilized from the sense strand of the gene, i.e., the strand which encodes the amino acid sequence of SEQ ID NO:2, expression of the encoded amino acid sequence will result. If sequences from the complementary (antisense) strand are utilized, then upon transcription from the promoter, an RNA will be produced which is complementary to native mRNA encoding hFAST-1. Antisense hFAST-1 oligonucleotides can be used to decrease expression of hFAST-1. Optionally, the recombinant construct or vector can also comprise a transcription terminator, in which case the inverted hFAST-1-derived sequence is located between the promoter and transcription terminator.

The invention also provides recombinant constructs and double-stranded DNA fragments which can be used, for example, in binding or transcriptional activating assays, using hFAST-1. A recombinant construct of the invention can comprise a reporter gene under the control of an activin response element. The activin response element comprises an hFAST-1 binding motif as shown in SEQ ID NO:4. Optionally, the recombinant construct can comprise a vector, as described above. Any reporter gene which produces a detectable product can be used. For example, the reporter gene can encode a non-human protein, such as green fluorescent protein, luciferase, chloramphenicol acetyltransferase, or β-galactosidase.

Double-stranded DNA fragments of the invention can comprise an activin response element. The activin response element includes an hFAST-1 binding motif, as shown in SEQ ID NO:4. Optionally, the double-stranded DNA fragment can be covalently attached to an insoluble polymeric support, such as a tissue culture plate, slide, or nylon membrane.

Any polynucleotide or oligonucleotide of this invention can be labeled using standard methods to facilitate detection. For example, polynucleotides or oligonucleotides can be radiolabeled with ³²P or covalently linked to a fluorescent or biotinylated molecule.

The invention provides methods for screening for test compounds which decrease or augment TGF-β activity. Compounds which decrease or augment TGF-β activity can be used to modify or regulate transcriptional activation associated with the TGF-β signaling pathway. Such compounds can be applied therapeutically, for example, to alter the growth of tumor cells or to alter normal or abnormal developmental processes.

Test compounds can be selected from natural substances secreted, extracted, isolated, or purified from microbes, plants, or animals, or can be synthetic agents. The test compounds can be pharmacologic agents already known in the art or can be compounds previously unknown to have any pharmacological activity.

In one embodiment of the invention, a test compound is contacted with a first protein and a second protein. The first protein comprises all or a portion of Smad2, or a naturally occurring biologically active variant thereof, which is capable of binding to hFAST-1. The second protein comprises all or a portion of hFAST-1, or a naturally occurring biologically active variant thereof, which is capable of binding to the portion of the Smad2 protein. Contacting can occur in vitro. The first and second proteins can be produced recombinantly, isolated from human cells, or synthesized by standard chemical methods. The binding sites can be located on fill-length proteins, fusion proteins, or polypeptides. If desired, the test compound can be contacted with one of the two proteins prior to contacting with the other protein. Optionally, the step of contacting can also be performed by contacting a test compound with a cell which expresses the first and second proteins. The cell can be a normal human cell, for example, a breast, colon, thymus, or muscle cell, or can be a related cell line.

Binding or dissociation of the first and second proteins in the presence of the test compound can be determined by measuring any of the following amounts: (a) the first protein which is bound to the second protein, (b) the second protein which is bound to the first protein, (c) the first protein which is not bound to the second protein, or (d) the second protein which is not bound to the first protein. The amount of a complex formed by the first and second proteins can also be determined. The first or second protein can be radiolabeled or labeled with fluorescent or enzymatic tags and can be detected, for example, by scintillation counting, fluorometric assay, monitoring the generation of a detectable product, or by measuring the apparent molecular mass of the bound or unbound proteins by gel filtration or electrophoretic mobility. Either the first or second protein can be bound to a solid support, such as a column matrix or a nylon membrane.

A test compound which decreases the amount of (a) or (b) or which increases the amount of (c) or (d) is a candidate compound for inhibiting the action of TGF-β. Preferably, the test compound decreases the amount of (a) or (b) or increases the amount of (c) or (d) by at least 30-40%, more preferably by at least 40-60%, 50-70%, 60-80%, 70-90%, 75-95%, or 80-98%.

In another embodiment, test compounds can be screened for their ability to decrease or augment TGF-β related activity. A cell is contacted with a test compound and with TGF-β. The cell comprises all or a portion of Smad2 protein, or a biologically active variant thereof, which is capable of binding to hFAST-1. The cell also comprises all or a portion of hFAST-1 protein, or a biologically active variant thereof which is capable of binding to Smad2. The cell also comprises hSmad4 protein.

Smad2, hFAST-1, and hSmad4 proteins or polypeptides can be supplied to the cell, for example, by transfecting the cell with DNA constructs which encode these proteins or polypeptides. Alternatively, cell types which normally contain one or more of the proteins or polypeptides can be used, such as normal breast, colon, thymus, or muscle cells, or related cell lines.

The cell also comprises a vector. The vector comprises a reporter gene under the control of an ARE. The ARE comprises a DNA motif (hFAST-1 binding domain) as shown in SEQ ID NO:4. By measuring the level of transcription or expression of the reporter gene using standard methods, the effect of the test compound can be determined. A test compound which increases the amount of reporter gene transcription or expression is a potential drug for augmenting TGF-β activity, and a test compound which decreases the amount of reporter gene transcription or expression is a potential drug for decreasing TGF-β activity. Preferably, the test compound increases or decreases the amount of transcription or expression of the reporter gene by at least 30-40%, more preferably by at least 40-60%, 50-70%, 60-80%, 70-90%, 75-95%, or 80-98%.

In another embodiment of the invention, a two hybrid method can be used to evaluate the binding of all or portions of hFAST-1 with other proteins such as Smad2. A cell can be contacted with a test compound to screen for drugs which have the ability to decrease or augment TGF-β activity.

The cell comprises two fusion proteins, which can be provided to the cell by means of expression constructs. The first fusion protein comprises either a DNA binding domain or a transcriptional activating domain and all or a portion of an hFAST1 protein or a naturally occurring biologically active variant of hFAST-1. The portion of hFAST-1 consists of a contiguous sequence of amino acids selected from the amino acid sequence shown in SEQ ID NO:2 and is capable of binding to Smad2. The portion of hFAST-1 can be selected so that it comprises neither a DNA binding domain nor a transcriptional activation domain. The second fusion protein comprises either a DNA binding domain or a transcriptional activating domain and all or a portion of Smad2 or a naturally occurring biologically active variant of Smad2. The portion of Smad2 is that portion which is capable of binding to hFAST-1. If the first fusion protein comprises a transcriptional activating domain, the second fusion protein comprises a DNA binding domain. On the other hand, if the first fusion protein comprises a DNA binding domain, the second fusion protein comprises a transcriptional activating domain.

The cell also comprises a reporter gene comprising a DNA sequence to which the DNA binding domain specifically binds. When the portion of hFAST-1 and the portion of Smad2 bind, the DNA binding domain and the transcriptional activating domain will be in close enough proximity to reconstitute a transcriptional activator capable of initiating transcription of the detectable reporter gene in the cell. The expression of the reporter gene in the presence of the test compound is then measured. A test compound which decreases expression of the reporter gene is a potential drug for increasing TGF-β activity. A test compound which decreases the expression of the reporter gene is a potential drug for decreasing TGF-β activity. Preferably, the test compound increases or decreases reporter gene expression by at least 30-40%. More preferably, the test compound increases or decreases reporter gene expression by at least 40-60%, 50-70%, 60-80%, 70-90%, 75-95%, or 80-98%.

Many DNA binding domains and transcriptional activating domains can be used in this system, including the DNA binding domains of GAL4, LexA, and the human estrogen receptor paired with the acidic transcriptional activating domains of GAL4 or the herpes virus simplex protein VP16 (See, e.g., G. J. Hannon et al., Genes Dev. 7, 2378, 1993; A. S. Zervos et al., Cell 72, 223, 1993; A. B. Votjet et al, Cell 74, 205, 1993; J. W. Harper et al., Cell 75, 805, 1993; B. Le Douarin et al., Nucl. Acids Res. 23, 876, 1995). A number of plasmids known in the art can be constructed to contain the coding sequences for the fusion proteins using standard laboratory techniques for manipulating DNA (see Example 1, infra). Suitable detectable reporter genes include the E. coli lacZ gene, whose expression can be measured colorimetrically (e.g., Fields and Song, supra), and yeast selectable genes such as HIS3 (Harper et al., supra, Votjet et al., supra; Hannon et al., supra) or URA3 (Le Douarin et al., supra). Methods for transforming cells are also well known in the art. See, e.g., Hinnen et al., Proc. Natl. Acad. Sci. U.S.A. 75, 1929-1933, 1978.

The above disclosure generally describes the present invention. A more complete understanding can be obtained by reference to the following specific examples, which are provided herein for purposes of illustration only and are not intended to limit the scope of the invention.

EXAMPLE 1

Example 1 describes the isolation of the hFAST-1 gene.

Sequences corresponding to xFAST-1, but outside the forkhead domain, were used to search the National Center for Biotechnology Information (NCBI) nucleotide sequence database ‘dbest’ using the BLAST program ‘tblastn’. An EST sequence (accession # AA218611) was identified based on its homology with the Smad interaction domain of xFAST-1. Primers were designed to extend the EST sequence using a RACE method. Briefly, nested PCR was performed using CLONTECH's Marathon-ready Human Colorectal Adenocarcinoma cDNA as the initial template and a set of EST-specific primers in combination with the AP1 or AP2 primers provided with the Marathon-ready cDNA. After two rounds of PCR amplification, the PCR products were gel-purified and sequenced using Thermo Sequenase (Amersham).

To ensure the correctness of the sequence, the sequences of multiple independent PCR products from cDNA and genomic DNA were determined. Multiple stop codons in all three reading frames were identified at both 5′ and 3′ ends of the PCR products and used to derive a long ORF defining hFAST-1. The first in-frame methionine in this ORF was assumed to be the initiation site for translation, and the sequences surrounding this methionine matched the Kozak consensus (Kozak, 1992).

A sequence alignment between hFAST-1 and xFAST-1 was carried out using the MACAW multiple alignment software (v2.01). The results are shown in FIG. 1. The coding sequence of the hFAST-1 gene is shown in SEQ ID NO:1. The corresponding amino acid sequence is shown in SEQ ID NO:2.

The hFAST-1 and xFAST-1 genes are considerably divergent. There are only two regions of significant similarity between xFAST-1 and hFAST-1, corresponding to the presumptive DNA-binding forkhead domain and the carboxyl terminal Smad-binding domain (FIG. 1). A prominent nuclear localization domain (hFAST-1 residues 22-30) was conserved at the amino-terminal end of the forkhead domain of both proteins.

EXAMPLE 2

Example 2 demonstrates expression of hFAST-1.

RT-PCR was performed with Platinum Taq DNA polymerase (GibcoBRL) and primers NT2-11 (5′-CTGGAAAGACTCCATTCG-3′; SEQ ID NO: 5) and NT2-8 (5′-CACAGAGGCCTCTCAGAAG-3′; SEQ ID NO: 6). These primers span an intron and thereby allow discrimination of mRNA-derived PCR products from those derived from genomic DNA or unprocessed RNA. The cDNA templates were prepared from total RNA of different normal tissues using SuperScript II reverse transcriptase (GibcoBRL) and random hexamers as primers (Thiagalingam et al., 1996).

The hFAST-1 gene appeared to be expressed in all normal human tissues tested, including those of breast, colon, thymus, and muscle, as well as in several cancer cell lines FIG. 2A).

EXAMPLE 3

Example 3 demonstrates chromosomal mapping of the hFAST-1 gene.

A genomic clone containing hFAST-1 was obtained by screening a bacterial artificial chromosome (BAC) library. This clone was used in fluorescence in situ hybridization (FISH) analyses of human metaphase spreads, revealing that the hFAST-1 gene resided at chromosome 8q24.

For chromosomal mapping of the hFAST-1 gene, two independent BAC clones containing the hFAST-1 gene were labeled with biotin-16-dUTP by nick translation. Human prometaphase chromosome spreads were fixed on slides and pretreated with RNase and pepsin. Multicolor FISH was performed as described (Lengauer et al., 1997). Hybridization signals were detected with FITC Avidin-DCS (Vector), and chromosomes were counterstained with DAPI. The resulting banding pattern and hybridization signals were evaluated by epifluorescence microscopy with a Nikon Eclipse E800.

Fifty randomly selected prometaphases were evaluated for each clone, and each of them showed hybridization signals on the distal long arm of both chromatids at chromosomal region 8q24.3. The chromosomal location was confirmed by double hybridization of hFAST-1 sequences and a centromere probe specific for chromosome 8 (Dunham et al., 1992). Fine-mapping of hFAST-1 to the 8q24.3 band was confirmed by fractional length measurements (Lichter et al., 1990).

EXAMPLE 4

This example demonstrates sequence analysis of hFAST-1 in colon cancer cells.

Many studies have shown that TGF-β responsiveness is abrogated during tumorigenesis (Fynan and Reiss, 1993). To determine whether the hFAST-1 gene was commonly altered in cancers, its sequence was examined in 45 colorectal cancer cell lines passaged in vitro or as xenografts in nude mice. For this purpose, the structure and sequence of the gene were determined from PCR analyses of genomic DNA and cDNA, revealing two small introns, at codons 58/59 and 93/94, respectively. Genomic DNA was PCR-amplified with primers NT2-12 (5′-CCCCCTTCCATCCGAATG-3′; SEQ ID NO:7) and NT2-3 (5′-GAGCTGCTGTGTCGCAGAC-3′; SEQ ID NO: 8). This amplification resulted in a 1750 bp PCR product containing the entire coding region of hFAST-1 plus its two introns. After gel purification, the PCR products were sequenced using Thermo Sequenase (Amersham). Complete sequence determination of the coding sequence plus the two introns in the 45 tumors revealed no variations from the wild-type sequence other than three polymorphisms (one silent change at codon 150, one serine to threonine substitution at codon 113, and one threonine to serine substitution at codon 125).

EXAMPLE 5

This example demonstrates interaction of hFAST-1 with Smad2.

To determine whether hFAST-1, like its Xenopus counterpart, would bind to Smad2, ³⁵S-labeled proteins were generated through in vitro transcription and translation of an hFAST-1 cDNA clone. A plasmid (pGST-Smad2/MH2) expressing the carboxyl terminus of Smad2 (codons 183-467, comprising the MH2 domain (Riggins et al., 1997)) fused to GST was constructed as previously described (Zawel et al., 1998). Full-length hFAST-1 was PCR-amplified with primers NT2/flag-TNT1 (5′-GGATCCTAATACGACTCACTATAGGGAGACCACCATGGA CTACAAGGACGACGATGACAAGGGGCCCTGCAGCGGCTCC-3′; SEQ ID NO:9) and primer NT2-3. A C-terminal fragment of hFAST-1 was amplified with primers NT2/flag-TNT2 (5′-GGATCCTAATACGACTCACTATAGGGAGACCACCATGGACTACAAG GACGACGATGACAAGCCCCTTCCTGGCCCCACGAG-3′; SEQ ID NO:10) and primer NT2-3. As a control, the entire ORF of PIG3 (Polyak et al., 1997) was also PCR-amplified.

These PCR products were used as templates in an in vitro transcription and translation (TNT) reaction using TNT®T7 Coupled Reticulocyte Lysate System (Promega). The ³⁵S-labeled TNT products were incubated with the GST-Smad2/MH2 fusion protein coupled to agarose beads for 2 hours at 40° C. in EBC buffer (50 mM Tris-HCl, pH 7.5, 100 mM NaCl, 0.5% NP-40). After five washes with EBC buffer at room temperature, the agarose beads were collected by brief centrifugation and the bound proteins eluted by boiling in SDS-sample buffer. The eluted proteins were separated in a 4-20% Tris-glycine gel and autoradiography was performed.

The labeled proteins were incubated with agarose beads linked to the carboxyl-terminal MH2 domain of human Smad2, previously shown to bind xFAST-1 (Chen et al., 1997; Liu, 1997). Both full length hFAST-1 and a C-terminal fragment of hFAST-1 containing residues 221 to 365 bound efficiently and specifically to the MH2 domain of Smad2, demonstrating that Smad2-binding is a conserved property of FAST-1 proteins (FIG. 2B).

EXAMPLE 6

This example demonstrates hFAST-1 mediated transcriptional activation.

In order to determine whether hFAST-1 could function in vivo as a signal transducer for TGF-β, an expression vector was constructed in which hFAST-1 was under the control of the CMV promoter (pCMV-hFAST-1). To construct the vector, normal human colon cDNA was used as the template to PCR-amplify the hFAST-1 ORF with primers NT2-exp5′ (5′-TATGCGGCCGCCACCATGGGGCCCTGCAGCG-3′; SEQ ID NO:11) and NT2-exp3′ (5′-TATGCGGCCGCGAGCTGCTGTGTCGCAGAC-3′; SEQ ID NO:12). The PCR product was cloned into the Not1 site of pCI-neo (Promega) and the recombinant plasmid (pCMV-hFAST-1) sequenced to ensure its integrity. Transfection was carried out as described (Zhou et al., 1998).

pCMV-hFAST-1 was transfected into the mink lung epithelial cell line MvLu1 together with the AR3-lux reporter containing three copies of the activin response element (ARE) from the Xenopus Mix.2 promoter (Chen et al., 1996; Hayashi et al., 1997). The plasmid pAR3-lux was provided by J. Wrana (The Hospital for Sick Children, Toronto). AR3-lux was activated over 30-fold by hFAST-1, and this response was completely dependent on TGF-β exposure (FIG. 3A). A similar TGF-β-dependent activity of hFAST1 was observed in human HaCaT cells, another TGF-β responsive line.

In contrast to the AR3-lux reporter, cotransfection of the hFAST-1 expression vector had no effect on the activation of the TGF-β responsive reporters p3TP-lux or SBE4-lux. Expression of an activin receptor whose kinase was engineered to be constitutively active even in the absence of ligand (Attisano et al., 1996), also conferred high levels of AR3-lux activity in the presence of co-transfected hFAST-1 (FIG. 3B).

Human HCT116 cells were employed to examine other requirements for FAST-1-dependent activation of AR3-lux. The endogenous TGF-β receptor type II (RII) gene is mutated in these cells (Markowitz et al., 1995; Parsons et al., 1995), but TGF-β responses can be restored by exogenous expression of the RII gene (Wang et al., 1995; Zhou et al., 1998). The TGF-β RII expression vector has been described by Zhou et al. (1998). FIG. 3C shows that co-expression of the RII receptor was required for the TGF-β- and hFAST-1-dependent activation of AR3-lux.

To demonstrate that the activation of AR3-lux was dependent on the DNA-binding forkhead domain of hFAST-1, an hFAST-1 expression vector was generated in which a single residue within the forkhead domain was altered (arginine substituted for histidine at residue 83). Crystallographic studies of the HNF-3γ forkhead domain had shown that this histidine contacted DNA and would be expected to be critical for its activity (Clark et al., 1993). The results in FIG. 3C show that this arginine substitution totally abrogated hFAST-1 activity.

Finally, the hypothesis was tested that Smad4 is required for the hFAST-1 activation of AR3-lux. The 5-18 cell line is a derivative of HCT116 cells in which both alleles of Smad4 were disrupted by targeted homologous recombination (Zhou et al., 1998). Transfection of hFAST-1 into these cells resulted in little AR3-lux activity compared to the parental line (FIG. 3C). Thus the transcriptional activity of hFAST-1, even when overexpressed, was dependent on an intact endogenous Smad4 gene.

EXAMPLE 7

This example demonstrates sequence-specific DNA binding of hFAST-1.

Forkhead proteins are known to bind DNA in a specific fashion, with the loose consensus sequence (G/A)(T/C)(C/A)AA(C/T)A (Kaufmann and Knochel, 1996; SEQ ID NO:13). The xFAST-1 protein was discovered on the basis of its binding to the ARE within the promoter of the activin-inducible Mix.2 gene, and the responsible sequences were mapped to a six bp sequence (AAATGT) which was repeated twice within the ARE but which was not very similar to the forkhead consensus (Chen et al., 1996). To define the DNA sequences which could bind to hFAST-1, oligonucleotides were selected which could bind to the protein from a random pool. The oligonucleotides were degenerate in a 20 bp central region and were flanked on each side by 20 bp regions of known sequence. The hFAST-1-DNA complexes were separated by EMSA and the recovered DNA amplified by PCR. Following three rounds of selection and amplification, recovered oligonucleotides were cloned and individually tested for binding to hFAST-1 in EMSA.

To produce a GST-fusion protein (FAST-FL) containing the full length hFAST-1, the entire ORF of hFAST-1 was PCR-amplified and cloned into the BamH1 site of pGEX2TK (Pharmacia). A GST-fusion protein (FAST-FH) containing only the forkhead domain of hFAST-1 was constructed similarly. GST-fusion proteins containing the MH1 or MH2 domains of Smad2 were produced as previously described (Zawel et al., 1998). Proteins produced in bacteria from these vectors were purified with glutathione-agarose and used to select random oligonucleotides as previously described (Zawel et al., 1998). In brief, following binding to 1 μg of GST-FAST-1 proteins (or following “mock” reactions without added protein), EMSA was performed and the location of the DNA-protein complexes within the gels was approximated based on the mobility of complexes generated with an ARE-derived probe (Chen et al., 1996). Gel slices were homogenized, incubated at 65 oC for 30 min, and then passed through Spin-X columns (Costar). Recovered oligonucleotides were extracted with phenol-chloroform, precipitated with ethanol, re-amplified, and subjected to the next round of binding. Following completion of the third selection-amplification cycle, PCR products were cloned into pZERO2.1 (Invitrogen).

Sixty bp probes corresponding to single clones were generated for EMSA by colony PCR using the following ³²P-labeled primers: 5′-TAGTAAACACTCTATCAATTGG-3′ (SEQ ID NO:14) and 5′-GTCCAGTATCGTTTACAGCC-3′ (SEQ ID NO:15). To determine the oligonucleotide sequences contained within single clones, inserts were amplified by colony PCR using M13 forward and reverse primers and the PCR products sequenced using Thermo Sequenase and an SP6 primer. To test binding to PCR products derived from clones, 1.0-1.5 μg protein (˜1 μM final concentration) and 50 ng of DNA (end-labeled to 2×10⁶ dpm/μg) were used. To test binding to chemically synthesized oligonucleotides (rather than those generated through PCR), complementary oligonucleotides were synthesized and labeled with γ³²P-ATP and T4 polynucleotide kinase prior to annealing. The sequence of the FBE oligonucleotide was 5′-CGGATTGTGTATTGGCTGTAC-3′ (SEQ ID NO:16), and the sequence of the control oligonucleotides (FBE*), containing two alterations of the FBE consensus, was 5′-CGGATTCTGTATCGGCTGTAC-3′ (SEQ ID NO:17). The sequence of the ARE oligonucleotide was 5′-TATCTGCTGCCCTAAAATGTGTATTCCA TGGAAATGTCTGCCCTTCTCTCCGTAC-3′ (SEQ ID NO:18). For binding to oligonucleotides, 0.3-0.5 μg of protein (μ0.4 μM final concentration) and 0.5 ng of DNA (end-labeled to 2×10⁸ dpm/μg) was used.

The inserts from 22 of 23 recovered clones bound to hFAST-1 (FIG. 4A). Comparison of the sequences of clones exhibiting hFAST-1 binding revealed a striking consensus (FIG. 4B). All clones contained two invariant three base elements separated by two G or T residues. The inferred consensus was TGT(G/T)(G/T)ATT (FIG. 4B; SEQ ID NO:4). To test whether this 8 bp consensus could indeed mediate hFAST-1 binding, an oligonucleotide containing a single copy of it was synthesized and tested in EMSA. This oligonucleotide (FBE, for FAST-1 binding element) bound efficiently to purified full length hFAST-1 protein and also (though less well) to the forkhead domain of hFAST-1 (FIG. 4C). FBE did not bind to similarly purified Smad2 proteins (FIG. 4C). An oligonucleotide in which two of the consensus positions were altered exhibited no binding to hFAST-1, documenting the specificity of the interaction (FIG. 4C).

The 8 bp consensus TGT(G/T)(G/T)ATT (SEQ ID NO:4) defined here was not related to the consensus ((G/A)(T/C)(C/A)AA(C/T)A; SEQ ID NO:13) inferred from the study of other forkhead proteins (Kaufmann and Knochel, 1996). Interestingly, the ARE element from the Mix.2 promoter contains a perfect match (TGTGTATT) to the consensus defined here. This 8 bp sequence overlapped one of the two repeats (AAATGT) which Chen et al. (Chen et al., 1996) suggested might be responsible for xFAST-1 binding, but it is likely that the TGTGTATT sequence was actually responsible for this binding. Chen et al. performed an informative experiment with a variant of the ARE which did not bind xFAST-1 complexes. Importantly, one of the three altered residues in this non-binding variant coincidentally affected the second base of the 8 bp consensus noted above, changing it to TCTGTATT (changed residue underlined). To specifically test whether the FBE was the critical element of the ARE for binding to FAST-1, we synthesized two 50 bp oligonucleotides, one comprising the entire sequence of the ARE ((Chen et al., 1996; SEQ ID NO:10) and one comprising the identical sequence except for a single base substitution within the FBE (TCTGTATT instead of TGTGTATT). Only the wild type ARE sequence bound to FAST-1 (FIG. 4D).

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1. An isolated and purified hFAST-1 protein comprising the amino acid sequence shown in SEQ ID NO:2 and naturally occurring biologically active variants thereof.
 2. A fusion protein which comprises a first protein segment and a second protein segment fused to each other by means of a peptide bond, wherein the first protein segment consists of at least thirteen contiguous amino acids selected from the amino acid sequence shown in SEQ ID NO:2.
 3. An isolated and purified polypeptide which consists of at least thirteen contiguous amino acids of hFAST-1 as shown in SEQ ID NO:2.
 4. The isolated and purified polypeptide of claim 3 which binds to a Smad2 protein as shown in SEQ ID NO:3.
 5. The isolated polypeptide of claim 3 wherein the at least thirteen contiguous amino acids of hFAST-1 comprise amino acids 277-364 of SEQ ID NO:2.
 6. The isolated polypeptide of claim 3 wherein the at least thirteen contiguous amino acids of hFAST-1 comprise amino acids 221-365 of SEQ ID NO:2.
 7. A preparation of antibodies which specifically bind to an hFAST-1 protein as shown in SEQ ID NO:2.
 8. The preparation of antibodies of claim 7 wherein the antibodies are monoclonal.
 9. The preparation of antibodies of claim 7 wherein the antibodies are purified from an animal antiserum.
 10. The preparation of antibodies of claim 7 wherein the antibodies are affinity purified.
 11. A subgenornic polynucleotide which encodes an hFAST-1 protein as shown in SEQ ID NO:2.
 12. The subgenomic polynucleotide of claim 11 which is intron-free.
 13. The subgenomic polynucleotide of claim 11 which comprises the sequence shown in SEQ ID NO:1.
 14. A vector comprising the polynucleotide of claim
 11. 15. A vector comprising the polynucleotide of claim
 12. 16. A vector comprising the polynucleotide of claim
 13. 17. A recombinant host cell which comprises the polynucleotide of claim
 11. 18. A recombinant host cell which comprises the polynucleotide of claim
 12. 19. A recombinant host cell which comprises the polynucleotide of claim
 13. 20. A recombinant DNA construct for expressing hFAST-1 antisense nucleic acids, comprising: a promoter, and a coding sequence for hFAST-1 consisting of at least 12 contiguous base pairs selected from SEQ ID NO:1, wherein the coding sequence is in an inverted orientation with respect to the promoter, such that upon transcription from said promoter an RNA is produced which is complementary to native mRNA encoding hFAST-1.
 21. The construct of claim 20 further comprising a transcription terminator, wherein the coding sequence is between the promoter and the terminator.
 22. A method of screening test compounds for those which inhibit the action of TGF-β, comprising the steps of: contacting a test compound with a first protein which is all or a portion of a Smad2 protein or a naturally occurring biologically active variant thereof, wherein the portion of the Smad2 protein is capable of binding to hFAST-1, and a second protein which is all or a portion of hFAST-1 or a naturally occurring biologically active variant thereof, wherein the portion of hFAST-1 is capable of binding to the portion of the Smad2 protein; and determining an amount selected from the group consisting of: (a) the first protein bound to the second protein, (b) the second protein bound to the first protein, (c) the first protein which is not bound to the second protein, and (d) the second protein which is not bound to the first protein, wherein a test compound which decreases the amount of (a) or (b) or increases the amount of (c) or (d) is a candidate compound for inhibiting the action of TGF-β.
 23. The method of claim 22 wherein the step of contacting is performed in vitro.
 24. The method of claim 22 wherein the step of contacting is performed by contacting a test compound with a cell which expresses the first protein and the second protein.
 25. The method of claim 23 wherein the test compound is contacted with one of the two proteins prior to contacting with the other protein.
 26. The method of claim 23 wherein one of the two proteins is bound to a solid support.
 27. The method of claim 23 wherein at least one of the two proteins is radiolabeled.
 28. The method of claim 23 wherein at least one of the two proteins is a fusion protein.
 29. The method of claim 23 wherein at least one of the two proteins is a fusion protein that has a detectable enzyme activity.
 30. A method of screening test compounds for the ability to decrease or augment TGF-β activity, comprising the steps of: (a) contacting a cell with a test compound, wherein the cell comprises: i) a first fusion protein comprising (1) a DNA binding domain or a transcriptional activating domain and (2) all or a portion of an hFAST-1 protein, wherein the portion consists of a contiguous sequence of amino acids selected from the amino acid sequence shown in SEQ ID NO:2, wherein the portion is capable of binding to Smad2 protein; ii) a second fusion protein comprising (1) a DNA binding domain or a transcriptional activating domain and (2) all or a portion of Smad2 protein, or a naturally occurring biologically active variant thereof wherein the portion is capable of binding to hFAST-1 protein, wherein when the first fusion protein comprises a DNA binding domain, the second fusion protein comprises a transcriptional activating domain, and when the first fusion protein comprises a transcriptional activating domain, the second fusion protein comprises a DNA binding domain, wherein the interaction of the portion of the hFAST-1 protein with the portion of Smad2 protein reconstitutes a sequence-specific transcriptional activating factor, ii) a reporter gene comprising a DNA sequence to which the DNA binding domain of the first or second fusion protein specifically binds; and iv) hSmad4 protein; and (b) measuring the expression of the reporter gene, a test compound which increases the expression of the reporter gene being a potential drug for increasing TGF-β activity, and a test compound which decreases the expression of the reporter gene being a potential drug for decreasing TGF-β activity.
 31. A method of screening for drugs with the ability to decrease or augment TGF-β activity comprising the steps of: (a) contacting a cell with a test compound and with TGF-β, wherein the cell comprises: (i) all or a portion of Smad2 protein or a naturally occurring biologically active variant thereof, wherein the portion of Smad2 protein is capable of binding to hFAST-1; (ii) all or a portion of hFAST-1 or a naturally occurring biologically active variant thereof, wherein the portion of hFAST-1 is capable of binding to Smad2 protein; (iii) a vector which comprises a reporter gene under the control of an activin response element, wherein the activin response element comprises an hFAST-1 binding motif TGT(G/T)(T/G)ATT as shown in SEQ ID NO:4; and (iv) hSmad 4 protein; and (b) measuring transcription of the reporter gene, a test compound which increases the amount of reporter gene transcription being a potential drug for augmenting TGF-β activity, and a test compound which decreases the amount of reporter gene transcription being a potential drug for decreasing TGF-β activity.
 32. A recombinant construct which comprises a reporter gene under the control of an activin response element, wherein the activin response element comprises an hFAST-1 binding motif TGT(G/T)(T/G)ATT as shown in SEQ ID NO:4.
 33. The recombinant construct of claim 32 wherein the construct comprises a vector.
 34. The recombinant construct of claim 32 wherein the reporter gene encodes a non-human protein.
 35. The recombinant construct of claim 34 wherein the non-human protein is selected from the group consisting of green fluorescent protein (GFP), luciferase, chloramphenicol acetyltransferase, and β-galactosidase.
 36. A double-stranded DNA fragment which comprises an activin response element which comprises an hFAST-1 binding motif TGT(G/T)(T/G)ATT as shown in SEQ ID NO:4, wherein the fragment is covalently attached to an insoluble polymeric support.
 37. An isolated and purified oligonucleotide which encodes at least thirteen contiguous amino acids of hFAST-1 protein as shown in SEQ ID NO:2.
 38. An isolated and purified oligonucleotide which comprises at least 19 contiguous nucleotides of hFAST-1 as shown in SEQ ID NO:1.
 39. The isolated oligonucleotide of claim 38 which is radiolabeled.
 40. The isolated oligonucleotide of claim 38 which is fluorescently labeled.
 41. The isolated oligonucleotide of claim 38 which comprises a sense strand.
 42. The isolated oligonucleotide of claim 38 which comprises an antisense strand. 